Razor blades and processes for the preparation thereof

ABSTRACT

The present invention is concerned with steel razor blades having a fluorocarbon polymeric coating thereon and more particularly with processes for producing improved blades of that nature. Generally, the improvements are brought about by providing a thin, cubic iron oxide layer beneath the polymeric coating.

niied States Patent EFase lmbein et a1.

RAZQR BLADES AND PROCESSES FOR THE PREPARATION THEREOF Inventors: lrwin W. Flschbein; Francis E. Flnherty,

both of Canton; Edward P. McLaughlin, Braintree; Fred T. Wlllett, Norwood, all of Mass.

Assignee: The Gillette Company, Boston, Mass.

Filed: June 7, 1967 Appl. No.: 644,052

US. Cl ..l48/6.35, 30/346.53, 30/346.54, 117/75, 117/132 CF Int. Cl ..B44d 1/36 Field of Search ..148/6.35; 117/132 CF, 75; 30/346.53, 346.54

1451 Mar. 28, 1972 Primary Examiner-Alfred L. Leavitt Assistant Examiner-Wm. E. Ball Attorney-Philip Colman, Oistein J. Bratlie and William M. Anderson 57 ABSTRACT The present invention is concerned with steel razor blades having a fluorocarbon polymeric coating thereon and more particularly with processes for producing improved blades of that nature. Generally, the improvements are brought about by providing a thin, cubic iron oxide layer beneath the polymeric coating.

RAZOR BLADES AND PROCESSES FOR THE PREPARATION THEREOF U.S. Pat. No. 3,071,856 to Irwin W. Fischbein discloses processes for substantially improving the shaving properties (e.g., shaving comfort) of razor blades through a reduction in pull by applying a fluorocarbon polymeric coating to the cutting edge. Generally, such processes comprise applying a suitable fluorocarbon coating composition, e.g., an aqueous dispersion, to the cutting edge and sintering the resulting coating at an elevated temperature to coalesce the particles into a substantially continuous film and adhere it to the substrate. In the past it has been proposed to carry out the sintering step in air, in a vacuum or in protective atmospheres such as inert gases, e.g., argon, nitrogen, etc., or reducing gases such as hydrogen, cracked ammonia, etc.

One object of the present invention is to provide razor blades and particularly carbon steel blades having fluorocarbon coatings thereon which blades have extended use life.

Another object of the present invention is to provide processes for producing such blades.

Still other objects of the present invention will appear from the following detailed description.

In the present invention it has been found that if a thin cubic iron oxide layer is present on the cutting edge under the fluorocarbon polymeric coating, the resulting blades surprisingly have a longer useful life during which the benefits derived from such coatings are enjoyed. The extended life is particularly noticeable with carbon steel blades wherein the benefits derived from such fluorocarbon coatings are appreciated for up to about 40 to 100 percent more shaves.

Generally, the blades upon which the processes of the present invention will be carried out will have wedged-shaped cutting edges, the included angle of which will usually lie between about to 35. The faces of such wedged-shaped cutting edges may extend back from the ultimate edge as much as 0.25 cm. or more and may comprise a single, uninterrupted, continuous facet or a plurality of facets formed by successive grinding and honing operations. The ultimate edge will usually have a thickness of less than 0.6 microns and preferably less than 0.25 microns. The solid fluorocarbon polymeric coatings which are applied to the cutting edge may extend over the entire wedge faces or at a minimum will usually cover at least a major portion of the zones immediately adjacent the ultimate edge. In preferred embodiments such zones will begin at the ultimate edge or within a micron or less from it and extend back from it for a distance of about 50 microns or more. The fluorocarbon coatings will usually be in the neighborhood of from about 0.1 to 0.3 microns in thickness.

When the present invention is used on carbon steel blades,

best results are obtained on blades such as described in the copending application Ser. No. 534,651 filed Mar. 16, 1966 in the name of Francis E. Flaherty which have retained austenite contents of at least 23 percent and have included angles between about 25 to 35 and preferably about 28.

Processes for forming cubic oxide layers on steel are known. Suitable processes, for example, are disclosed in the Journal of the Electrochemical Society, Vol. l 12, No. 6, pages 539-546, by W. E. Boggs, R. H. Kachik and G. E. Pellissier. Generally, such oxides are produced under mildly oxidizing conditions using, for example, reduced oxygen pressures at limitedly elevated temperatures for carefully controlled periods of time. Under such mildly oxidizing conditions, the cubic oxide magnetite (F e 0 is initially formed on the outer surface of the steel. As the oxidation continues it is believed a series of transition oxides, also of a cubic nature, begin to form at the magnetite-oxygen interface until ultimately a layer of the cubic oxide maghemite ('y-Fe O forms at such interface. If the oxidation is continued, eventually non-cubic a-Fe O begins to nucleate in the maghemite and a layer of the noncubic a-Fe O is ultimately formed on the outer surface.

Blades having a cubic iron oxide surface layer on their cutting edges may be produced by stopping the above described oxidation in any of the cubic stages before the a- TABLE I Period during which cubic Oxide outer layers will be i 0, Pressure Temperature Forming l. 0.01 torr to 220 C. (428 F.) Up to at least 10 torr I50 minutes (a torr equals about I mm. of Hg) 2. I00 torr 220 C. (428 F.) Up to at least 20 minutes 3. 0.0] ton to 270 C. (5l8 F.) Up to at least 10 torr 30 minutes 4. 0.0] torr 350 C. (662 F.) Up to about 5 minutes Cubic oxides of iron, when viewed under an electron microscope, are characterized by having a smooth, finegrained structure and are readily distinguishable from the a- Fe 0 which is rhombohedral and has a coarse-grained herringbone-like structure. Accordingly, one will have little trouble in finding the conditions best suited to his particular needs informing the cubic oxide on the cutting edges. in preferred embodiments of the present invention, the oxide immediately underlying substantially the entire fluorocarbon coating on the cutting edge is essentially of the cubic nature. it should be appreciated, however, that as long as the oxide immediately underlying at least a major portion of such coating, e.g., at least 50 percent of its area, and more particularly a predominance, e.g., at least 75 percent of its area, is of the cubic nature some of the benefits of the present invention will be realized.

The improvements provided by the present invention begin to become particularly noticeable when the cubic oxide layer is at least about 50 A. in thickness. The optimum thickness range generally lies between about 50 A. to 800 A. and more preferably between about 50 to 400 A. Thicker layers may be employed but it should be kept in mind that the quality of at least the first shave may begin to be adversely affected as the thickness increases.

When the cubic oxides are formed on stainless steel blades, a portion of the iron atoms in the cubic structure will be replaced by chromium atoms. The term cubic iron oxides" as used herein is intended to include such structures.

In addition to the cubic iron oxides mentioned above there is still another type known; namely, ferrous oxide (FeO). This oxide exists only above 570 C. and is not intended to beincluded in the term cubic iron oxide" as used herein.

In carrying out the processes of the present invention the cubic oxides may be formed on the cutting edges as they come from the sharpening process without requiring any further treatment such as hydrogen-stripping or electropolishing. Moreover, the oxides may be formed prior to, subsequent to or currently with the sintering of the fluorocarbon coating on the edges. In a preferred embodiment the cubic oxides are formed currently with the sintering step by carrying out such step in a limitedly oxidizing atmosphere. When the cubic 0xides are formed on the blade edge prior to the sintering step, the sintering should preferably be carried out in a vacuum or in an inert atmosphere so as not to alter or remove the previously formed cubic oxide layer..When the cubic oxides are during the sintering step, the amount of oxygen present in such mixed atmospheres will generally be less than 100 p.p.m. and more particularly less cubic oxide layer may be of adequate thickness and be formed in a reasonable amount of time, it is preferable that the mixture contain at least about 0.5 p.p.m. of oxygen. The preferred range of oxygen in the mixture will lie between about 0.5 to about 50 p.p.m. and more particularly between about I to 25 p.p.m. Generally, when more than p.p.m. of oxygen is present in the inert gas, the resulting blades may have a light brown to gold discoloration. Although such discoloration does of the blades, it may, in cerundesirable from a purely 250 microns and more particularly less than about 125 microns. The preferredreduced pressure range when air is used will generally be between about 0.2 microns to 125 pressures will usually be about one-fifth of those for air.

When the cubic oxide layer is formed concurrently with the sintering step, the reaction conditions are further dependent blade edges at temperatures between about 600 to 750 F. and more particularly between about 625 to 700 F. in periods of about 2 to minutes. Within theseconditions of time and temperature, it is usually advisable in carrying out the sintering and oxide-forming steps concurrently to use the lower oxygen pressures set forth above at the higher sintering temperatures and/or longer sintering times.

The cubic oxide layer may be formed subsequent to the sintering steps by employing conditions such as those set forth above for carrying out the sintering and oxide-forming steps concurrently.

Subsequent to forming the cubic oxide layer at an elevated temperature, the blades should usually be cooled to room temoxidizing or inert atmosphere before gases are nitrogen, argon, carbon dioxide and steam. The latter two gases, i.e., carbon dioxide and steam, are not generally inert with respect to steel at all temperatures, but at the relatively low temperatures which are used to form the blade edges such gases act as if they were essentially inert and may be employed.

than 50 p.p.m. In order that the Illustrative useful reducing gases are hydrogen and cracked ammonia. When a reducing gas is used as the protective gas, it would be expected because of the much larger amounts of it expectation, the cubic oxide layer can be suitably formed. Apparently, in the temperature ranges mentioned above, oxidation can be made to overcome the reducing effect of reducing atmospheres such as hydrogen if sufiicient oxygen is present in the mixture. This amount of oxygen will vary with temperature. At about 650 F., the amount of oxygen will usually be, for example, at least about 15 p.p.m. and generally will be Generally, the fluorocarbon polymers which are used in the present invention are solid, addition polymers comprising a plurality of CF,CF segments such as disclosed in the above mentioned US. Pat. No. 3,071,856. The preferred fluorocarbon polymers are those which comprise a preponderance of -CF CF segments such as polytetrafluoroethylene and copolymers tetrafluoroethylene with minor amounts e.g., 5 percent by weight of other monomers such as hexafluoropropylene. The molecular weight of the polymers may vary ranging, for example, from about 2,000 or even lower to above 2,000,000. Especially useful results were obtained polytetrafluoroethylene telomers such as disclosed in Irwin W. Fischbein's copending application Ser. No. 384,805 filed July 23, 1964 which are terminated by radicals comprising groups such as hydrogen, chlorine, methyl, hydroxymethyl, carboxyl, etc. When using such telomers, it is best to form the cubic oxide layer prior to or concurrently with the sintering step because the sintered polymeric films have a high degree of continuity and thus tend to be less permeable to the limitedly oxidizing gases.

The following non-limiting examples illustrate the processes of the present invention.

EXAMPLE I One hundred and twenty carbon steel blades were mechanically sharpened, cleaned in trichloroethylene and coated with Vydax 1000, a polytetrafluoroethylene Telomer sold by du- Pont. When the volatile vehicle of the coating composition had been evaporated, were placed in an all glass cassette within a glass chamber about 15 cu. in. in volume. The chamber was evacuated at room temperature to less than 50 millirnicrons H, pressure and a controlled air leak for producing 34 microns pressure in the chamber was set up and then isolated from the chamber by closing a valve. The chamber was again evacuated to a high vacuum, i.e., the millimicron range and the blades were brought to and maintained at a sintering temperature of about 640 F. through radiant heat from a hot salt bath surrounding the chamber. The preset TABLE II No. of shaves during which the benefits derived from the fluorocarbon coatings were appreciated sintering Atmosphere l. Limitedly 0xidizing(Example l) 6 shaves using 2. Hydrogen 3 3. Hydrogen (subsequently cooled from 300 F. to room temp. in air) 4. Argon gas 5. High vacuum (millimicron range) 4 shaves shaves shaves shaves EXAMPLE II a. Two hundred carbon steel blades which had been mechanically sharpened and cleaned in trichloroethylene were coated with an aqueous polytetrafluoroethylene dispersion and pre-dried at 210 F. for 30 minutes.

b. Thirty-five of the above coated blades were placed in a cassette and heated in hydrogen to 650 F. in about a 5 'minute period. The blades were held at 650 F. in the hydrogen for minutes and were then cooled to room temperature under hydrogen.

c. Another 35 of the blades, coated in paragraph a) were placed in a cassette and heated in a nitrogen atmosphere comprising 5.7 parts of oxygen to 650 F. in a 15 minute period. The blades were held in the nitrogen-oxygen atmosphere for 15 minutes at 650 F. and then cooled to room temperature in the same atmosphere.

The blades which were prepared according to the procedures set forth in paragraphs (b) and (c) above were shave tested and it was found that the blades which were cured in the nitrogen-oxygen atmosphere were rated higher over a significantly larger number of shaves than those cured in hydrogen.

The cubic oxides which are formed on the blade edges in the processes of the present invention may be removed for study and identification, e.g., under the electron microscope, by methods such as disclosed in The Isolation and Examination of Films from Metal Surfaces; an Improved Technique by T. F. Norse and F. Wormwell, Journal of Applied Chemistry, Vol. 2, pp. 550-554 (1952). The fluorocarbon films may be removed prior to the cubic oxides by soaking the blades in a dispersion of sodium in naphthalene for about 30 minutes.

In the past, thin, e.g., usually less than 30 A., cubic oxide layers may have been incidentally and unintentionally present on the sharpened edges of fluorocarbon coated blades. Such thin coatings do not provide the substantial improvement in shaving properties which are brought about by the thicker cubic oxide layers of the present invention.

Having thus described the invention, what is claimed is:

1. In a process of applying a fluorocarbon polymeric coating to a steel blade cutting edge and sintering the coating to adhere it to the edge the improvement consisting of forming at some time during the process a cubic iron oxide layer over at least a major portion of the surface area immediately underlying said fluorocarbon polymer coating on said cutting edge, said cubic iron oxide layer being at least about 50 A. in thickness.

2. A process as defined in claim 1 wherein said blade is a carbon steel blade.

3. A process as defined in claim 1 wherein said cubic iron oxide layer is in the range of about 50 to 800 Angstroms in thickness.

4. A process as defined in claim 1 wherein essentially the entire surface area immediately underlying said fluorocarbon polymer coating on said cutting edge is covered by said cubic iron oxide.

5. A process as defined in claim 1 wherein said blade is a carbon steel blade and said cubic iron oxide layer is in the range of about 50 to 800 Angstroms in thickness.

6. A process as defined in claim 1 wherein the fluorocarbon polymeric coating is polytetrafluoroethylene.

7. A process as defined in claim 1 wherein said cubic iron oxide layer is formed during the sintering step by carrying out said sintering in a limitedly oxidjzin atmosphere.

8. A process as defined in claim wherein the blade is a carbon steel blade and the cubic oxide is in the range of about 50 to 800 Angstroms in thickness.

9. A process as defined in claim 1 wherein said cubic oxide layer is formed prior to the sintering step.

10. A process as defined in claim 1 wherein said cubic oxide layer is formed subsequent to the sintering step.

1 1. In a process of applying a fluorocarbon polymeric coating to a steel blade cutting edge and sintering the coating to adhere it to the edge, the improvement of carrying out the sintering step in a slightly oxidizing atmosphere at a temperature between 600 and 750 F. for a time which will provide a cubic iron oxide layer in a range of about 50 to 800 Angstroms in thickness over a major portion of the surface of the cutting edge immediately underlying said fluorocarbon polymeric coating. 

2. A process as defined in claim 1 wherein said blade is a carbon steel blade.
 3. A process as defined in claim 1 wherein said cubic iron oxide layer is in the range of about 50 to 800 Angstroms in thickness.
 4. A process as defined in claim 1 wherein essentially the entire surface area immediately underlying said fluorocarbon polymer coating on said cutting edge is covered by said cubic iron oxide.
 5. A process as defined in claim 1 wherein said blade is a carbon steel blade and said cubic iron oxide layer is in the range of about 50 to 800 Angstroms in thickness.
 6. A process as defined in claim 1 wherein the fluorocarbon polymeric coating is polytetrafluoroethylene.
 7. A process as defined in claim 1 wherein said cubic iron oxide layer is formed during the sintering step by carrying out said sintering in a limitedly oxidizing atmosphere.
 8. A process as defined in claim 7 wherein the blade is a carbon steel blade and the cubic oxide is in the range of about 50 to 800 Angstroms in thickness.
 9. A process as defined in claim 1 wherein said cubic oxide layer is formed prior to the sintering step.
 10. A process as defined in claim 1 wherein said cubic oxide layer is formed subsequent to the sintering step.
 11. In a process of applying a fluorocarbon polymeric coating to a steel blade cutting edge and sintering the coating to adhere it to the edge, the improvement of carrying out the sintering step in a slightly oxidizing atmosphere at a temperature between 600* and 750* F. for a time which will provide a cubic iron oxide layer in a range of about 50 to 800 Angstroms in thickness over a major portion of the surface of the cutting edge immediately underlying said fluorocarbon polymeric coating. 